Just get some velcro tape, and apply it over the magnets.

They do have wooden magnets - but they're very expensive and hard to come by.

This post was edited by Geoffrey_B on Tue, Oct 1, 13 at 14:30

Did you have any luck addressing this issue? I'm dealing with the same thing and wondering what you found to work best.

I got a magnetic plastic one and it falls off constantly. I just found one on Etsy that is metal and sticks with mounting tape that seems promising and better made: https://www.etsy.com/listing/1068763669/floor-vent-air-deflector-4x10-heavy-duty